1. Field of the Invention
This invention relates to a method for rebuilding a bearing system for automotive alternators.
2. Description of the Related Art
A problem has developed in the industry involving the Delco CS Series alternator adapted for General Motors cars and light trucks. These alternators area commonly called the CS 121 and the CS 130 alternator.
The problem is the failure rate of the slip ring end bearing, known in the industry as a 6000 class bearing, which is located at the rear of the alternator. General Motors requires the alternator drive belt to be tightened to very high tension (e.g. 125 ft-lbs.). This high tension is transmitted down the alternator shaft to the end bearing at the rear end placing a great radial load, as well as some thrust load upon this bearing. When placed under this load, the 6000 bearing inner race becomes out-of-round and failure occurs. In the industry, therefore, a need exists for a stronger long lasting bearing for this application. It has been calculated that as high 17% of these alternators installed as original equipment since 1985 have failed out of more than six million presently on the road. This figure may increase as additional driving mileage accumulates.
When the end bearing race begins to wear out of round, and well before failure, the alternator rotor begins to make an elliptical orbit which causes vibration. This vibration, in turn, may cause the internal voltage regulator to fail. The elliptical orbit of the rotor (which has about 0.014 in. clearance from the stator) causes it to rub on the stator thereby causing eventual failure of both the rotor and the stator.
When the end bearing fails completely, the alternator will lock up causing vehicle break-down. Lock up of the alternator may cause additional damage to other vehicle components.
The CS Series alternator was originally promoted as a "throw-away", or unrebuildable component. In practice, however, these alternators are being routinely rebuilt. In the industry, automotive alternator rebuilders are experiencing as high as 40% failure rate of rebuilds that leave the shop, mostly due to repeat end bearing failure, even though the original bearings had been replaced.